A multi-mode fiber optic link using a vertical cavity surface emitting laser (VCSEL) is a key component for short-distance interconnection between a server and a high-performance computer node in a data center and a storage network. With increase of services provided in the Internet and users, a scale of a data center and data traffic therein also increase, and there are development requirements for a high data transmission rate, a long transmission link, and a low-cost optical link network. This imposes a higher requirement on stability of a VCSEL as a light source and light source quality (that is, low-noise performance). Meanwhile, a VCSEL-based optical module packaging manner with lower costs is more welcome in the market.
Magnitude of output optical power of a VCSEL changes with increase in temperature and using duration. A method for stabilizing output optical power of a VCSEL is: taking a part of the output optical power for monitoring, and dynamically controlling a bias current of the VCSEL by using a closed-loop feedback circuit, to stabilize the output optical power.
An output spectrum of the VCSEL presents multi-mode and dual-polarization component characteristics. A mode selection structure, a structure that destroys mode field integrity, and a polarization-sensitive structure all destroy integrity of the output spectrum of the VCSEL. If any one of the foregoing structures exists in an optical path, noise of an optical signal is increased. Especially, when the VCSEL is in high-speed dynamic modulation, increased noise greatly limits a modulation rate and a transmission link length.
An integrally formed coupling module made of a polymer is used to replace a traditional Transistor Outline (TO) structure, which not only can omit multiple discrete components but also can simplify a coupling manufacturing process. Therefore, costs are greatly lowered. As shown in FIG. 1, FIG. 1 is a schematic diagram of a process of implementing optical power monitoring in an integrally formed coupling module in the prior art, and the integrally formed coupling module in the prior art includes: a surface HIJK, a surface ABCD, and a surface EFGH. An incident surface of the surface ABCD is parallel to an incident surface of the surface EFGH, and the surface ABCD and the surface EFGH form an air gap. In FIG. 1, an optical signal emitted from a laser is represented by an arrowed line segment; the optical signal is reflected on the surface HIJK to form an optical signal 2; a part of the optical signal 2 is reflected on the surface ABCD to form an optical signal 3; the optical signal 3 may be used to monitor power; the other part of the optical signal 2 is transmitted through the interface ABCD to form an optical signal 4; the optical signal 4 is refracted on the surface EFGH to form an optical signal 5 and propagation continues; then the optical signal 5 is propagated to an optical fiber and is output. In the integrally formed coupling module, a medium air interface and an air medium interface forming an air gap reflects and refracts light, so that multiple beams of light (for example, the optical signal 3 and the optical signal 5 in FIG. 1) may be formed. Because optical power of the two beams of light is in a fixed proportion, if the optical power of the optical signal 3 is known, the optical power of the optical signal 5 can be determined.
In a process of implementing the present invention, it is found that, in the prior art shown in FIG. 1, light reflection and refraction of a structure system formed by the medium air interface and the air medium interface are polarization-sensitive. In the prior art, the air gap is formed in an integral polymer structure, and then two extra surfaces: the surface ABCD and the surface EFGH are formed in a light propagation direction. The surface ABCD introduces polarized noise a into the optical signal 2 passing through the surface ABCD, and then polarized noise of the optical signal 4 is greater than polarized noise of the optical signal 2. The surface EFGH also introduces polarized noise b into the optical signal 4 passing through the surface EFGH. Because the surface ABCD and the surface EFGH that form the air gap are respectively parallel to incident surfaces formed by the optical signal 2 and the optical signal 4, directions of the polarized noise a and the polarized noise b are the same. For the optical signal 5, with respect to the optical signal 4, the introduced polarized noise b is enhanced and superposed based on the polarized noise a. Therefore, polarized noise of the optical signal 5 is greater than the polarized noise of the optical signal 4. A final result is that the polarized noise of the optical signal 5 is greater than the polarized noise of the optical signal 4, and the noise of the optical signal 4 is greater than the noise of the optical signal 2. Therefore, the medium air interface included in the integrally formed coupling module in the prior art accumulates polarization relevant characteristics of an optical signal that passes through the medium air interface. That is, the medium air interface and the air medium interface in the prior art form a polarization-sensitive structure. When the polarization-sensitive structure exists in a VCSEL optical path, noise of an optical signal increases, which limits a data transmission rate of a link and a transmission link length.